Internal combustion engines convert the chemical energy from a fuel into mechanical energy. The fuel may be petroleum-based, natural gas, another combustible material, or a combination thereof. Most internal combustion engines inject an air-fuel mixture into one or more cylinders. The fuel ignites to generate rapidly expanding gases that actuate a piston in the cylinder. The fuel may be ignited by compression such as in a diesel engine or through some type of spark such as the spark plug in a gasoline engine. The piston usually is connected to a crankshaft or similar device for converting the reciprocating motion of the piston into rotational motion. The rotational motion from the crankshaft may be used to propel a vehicle, operate a pump or an electrical generator, or perform other work. A vehicle may be a truck, an automobile, a boat, or the like.
Many internal combustion engines use a fuel injection system to deliver fuel to the cylinders. Fuel injection systems usually have a fuel injector for each cylinder. The fuel injector usually sprays a measured amount of fuel in the cylinder. In diesel engines, the fuel pressure typically is increased for injecting the fuel near or at the end of the compression cycle. Fuel injectors for diesel engines usually have actuating mechanisms such as a piston to increase the pressure of the fuel. The actuating mechanisms in the fuel injector may be mechanically or hydraulically activated and may be electronically controlled.
Some diesel engines use hydraulically activated electronically controlled unit injection (HEUI) fuel system to inject fuel into the cylinders. A HEUI fuel injection system generally has a fuel injector for each cylinder of the engine. Each fuel injector usually has a control valve, an intensifier, and a nozzle in an injector housing. The control valve starts and stops the fuel injection. The intensifier increases the fuel pressure. The nozzle controls the injection of fuel into the cylinder. The fuel injector generally has a cylindrical configuration with the control valve at one end, the intensifier in the middle, and the nozzle at the other end. The injector housing usually is mounted to the cylinder head of the engine.
To begin fuel injection, the control valve provides high pressure oil to the intensifier. The control valve has a poppet valve connected to an electric solenoid. When energized, the solenoid opens the poppet valve to permit high pressure oil to flow along a passageway into a piston chamber of the intensifier. The high pressure oil may have a pressure in the range of about 500 psi (3 MPa) through about 4,500 psi (31 MPa). When de-energized, the solenoid closes the poppet valve to end the fuel injection.
The intensifier uses the high pressure oil to increase the pressure of the fuel. The intensifier has a piston positioned in the piston chamber. The piston is connected to a plunger that is positioned in a fuel chamber. The high pressure oil entering the piston chamber causes the piston to move the plunger against the fuel in the fuel chamber. The movement of the plunger increases the pressure of the fuel significantly. The fuel pressure may reach a pressure in the range of about 15,000 psi (103 MPa) through about 25,000 psi (172 MPa). The high pressure fuel flows through another passageway to a needle valve in the nozzle.
The nozzle uses the high pressure fuel to control the fuel injection into the cylinder. The high pressure fuel causes the needle valve to open. The high pressure fuel then exits the nozzle through an orifice. The nozzle usually is positioned adjacent to the cylinder for the high pressure fuel to enter the cylinder.
During operation, a fuel injector's piston and other actuating-related components may become worn or scored. Other mechanical difficulties may develop. The difficulties may affect the performance fuel injector and thus the cylinder in the engine.
During engine repairs or maintenance, one or more fuel injectors may be replaced due to operating difficulties with a cylinder. Many service technicians use a vehicle's on-board computer to determine whether to replace a HEUI fuel injector. The on-board computer may determine a HEUI fuel injector needs to be replaced even though the fuel injector is working or can work properly. Cylinders with HEUI fuel injectors are difficult to diagnose using the vehicle's computers and other electronics. The computers typically make comparisons from cylinder to cylinder to determine which cylinders may be contributing less than the other cylinders. These comparisons are not very accurate regarding the fuel injectors because other factors may cause the poor cylinder performance. These factors include the mechanical condition of the engine, the fuel quality at the time of the test, and the like. Some technicians also may replace a fuel injector as part of a general diagnostic approach when there is any mechanical problem or concern with a cylinder. After replacement, the used fuel injector may not be reinstalled in the engine even when the cylinder continues not to work properly. There are fuel injector test devices for testing fuel injectors outside the engine. Many service technicians do not have access to these test devices. The test devices tend to be more expensive and may be bulky to use.